1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
|
/*
* Copyright © 2010 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
/**
* \file opt_if_simplification.cpp
*
* Moves constant branches of if statements out to the surrounding
* instruction stream, and inverts if conditionals to avoid empty
* "then" blocks.
*/
#include "ir.h"
namespace {
class ir_if_simplification_visitor : public ir_hierarchical_visitor {
public:
ir_if_simplification_visitor()
{
this->made_progress = false;
}
ir_visitor_status visit_leave(ir_if *);
ir_visitor_status visit_enter(ir_assignment *);
bool made_progress;
};
} /* unnamed namespace */
/* We only care about the top level "if" instructions, so don't
* descend into expressions.
*/
ir_visitor_status
ir_if_simplification_visitor::visit_enter(ir_assignment *ir)
{
(void) ir;
return visit_continue_with_parent;
}
bool
do_if_simplification(exec_list *instructions)
{
ir_if_simplification_visitor v;
v.run(instructions);
return v.made_progress;
}
ir_visitor_status
ir_if_simplification_visitor::visit_leave(ir_if *ir)
{
/* If the if statement has nothing on either side, remove it. */
if (ir->then_instructions.is_empty() &&
ir->else_instructions.is_empty()) {
ir->remove();
this->made_progress = true;
return visit_continue;
}
/* FINISHME: Ideally there would be a way to note that the condition results
* FINISHME: in a constant before processing both of the other subtrees.
* FINISHME: This can probably be done with some flags, but it would take
* FINISHME: some work to get right.
*/
ir_constant *condition_constant = ir->condition->constant_expression_value();
if (condition_constant) {
/* Move the contents of the one branch of the conditional
* that matters out.
*/
if (condition_constant->value.b[0]) {
ir->insert_before(&ir->then_instructions);
} else {
ir->insert_before(&ir->else_instructions);
}
ir->remove();
this->made_progress = true;
return visit_continue;
}
/* Turn:
*
* if (cond) {
* } else {
* do_work();
* }
*
* into :
*
* if (!cond)
* do_work();
*
* which avoids control flow for "else" (which is usually more
* expensive than normal operations), and the "not" can usually be
* folded into the generation of "cond" anyway.
*/
if (ir->then_instructions.is_empty()) {
ir->condition = new(ralloc_parent(ir->condition))
ir_expression(ir_unop_logic_not, ir->condition);
ir->else_instructions.move_nodes_to(&ir->then_instructions);
this->made_progress = true;
}
return visit_continue;
}
|
